1. Field of the Invention
The present invention relates to a chain casing for an engine and more specifically an engine chain casing for enabling a smooth lubricant recirculation within the engine including an idler sprocket and two chains.
2. Description of the Prior Art
To obtain higher engine performance in automotive vehicles, double overhead camshaft (DOHC) engines have been widely used, in which two different camshafts for driving intake and exhaust valves separately are mounted on a cylinder head. An example of DOHC engines is disclosed in Japanese Published Unexamined (Kokai) Patent Appli. No. 60-50208. In this document, as shown in FIG. 1, an idler sprocket 1 is rotatably disposed between two camshafts 2 supported on the cylinder head CYH and a crankshaft 3 supported on the cylinder block CYB, and further a first chain 4A is reeved around the crankshaft 3 and the idler sprocket 1 and a second chain 4B is reeved around the idler sprocket 1 and the two camshafts 2 in order to drive the two camshafts 2 by the crankshaft 3 via the idler sprocket 1. In the prior-art DOHC engine, a chain chamber CHC for accommodating the idler sprocket 1 and the first and second chains 4A and 4B is covered by a rocker cover 5 fixed to the upper portion of a cylinder head CYH, a head side chain casing 6 fixed to the front end of the cylinder head CYH, and a block side chain casing 7 fixed to the front end of a cylinder block CYB.
In the above-mentioned arrangement, however, since the second chain 4B reeved around the idler sprocket 1 and the camshafts 2 is located in front of the first chain 4A reeved around the idler sprocket 1 and the crankshaft 3, the head side chain casing 6 for covering the second chain 4B and the idler sprocket 1 projects frontward from the front end of the cylinder head, with a result that two flat shoulder (or stepped) portions A and B are formed under the camshafts 2 and the idler sprocket 1, respectively. Therefore, in the prior-art chain casing for an engine, there exists a problem in that lubricant to be returned to an oil pan is accumulated and dried at these shoulder portions A and B and therefore a sufficient quantity of lubricant is not recirculated through an oil pump (not shown) due to malsuction of the oil pump.